Hydrofoil boat with wave and cavitation control



R. VOGT Sept. 22 1964 HYDROFOIL. BOAT WITH WAVE AND CAVITATION CONTROL 2Sheets-Sheet 1 Filed March 11, 1965 INVENTOR. m. P/(lfifl raw Sept. 22,1964 R. VOGT 3,149,602

HYDROFOILBOAT WITH WAVE AND CAVITATION CONTROL Filed March 11, 1963 2Sheets-Sheet 2 n'oww now- INVENTOR. 02. F/(WAWD r047 JZMX M AGE/VTUnited States Patent 3,149,602 HYDPAGFOIL 30A? Wifti-I WAVE ANDQAVKTATIGN CQNTRGL Richard Vogt, Santa Barbara, Caiiii, assignor to TheBoeing Company, Seattie, Wash, a corporation of Deiaware v Eiuhstitutedfor abandoned application Ser. No. 126,846,

July 19, 1961. This application IvIlar. 11, 19b3, Ser- No. 265,311

1% Glaims. (Cl, lid- &5)

This invention pertains to a hydrofoil boat and means for maintainingthe boat at a particular distance above the water.

This is a substitute application for abandoned tion Serial No. 126,846filed July 19, 1961.

More specifically this invention pertains to a hydrofoil boat havingmeans for raising and lowering the boat relative to the surface of thewater between a position wherein-the boat is about to contact thesurface of the water and a position wherein the hydrofoils are at thecavitation line where cavitation of the hydrofoils result.

Herebefore hydrofoil craft with movable or controllable hydrofoilsutilized booms or boom mechanisms protruding out in front of the boat.Attached to these booms were either vanes or floats for ridingsubstantially on the surface of the water or a predetermined depth belowthe water as determined by the float boom mechanism. A typical hydrofoilboat of this type is shown in Patent US. 2,603,179. This type ofhydrofoil craft with hydrofoil control means is limited in speed becauseof the cumbersome and forwardly protruding boom or vane mechanism on thefront of the boat. Also, because the waves obviously affect this boommechanism, some type of damping mechanism would have tobe incorporatedin the control system for preventing undue periodic pitching, and formaintaining the boat steady. When flotsam or any other type of floatingdebris is encountered by the boom mechanism, destruction or damagethereof results.

Other unsuccessful types have been disclosed for controlling a hydrofoilboat such as disclosed in US. Patent 2,722,189 wherein two vanes areutilized on the bow which continually protrude down into the water andextend under the boat. This type has its limitations due to thecontinual and constant submersion of the forward vanes in the water andwhich vanes are affected by flotsam or other floating debris on thesurface of the water. Likewise this system is also directly affected byeach wave encountered by the hydrofoil craft for causing the boat torise and lower with each wave.

Accordingly a principal object of this invention is to provide ahydrofoil boat with hydrofoil control means comprising two means, onemeans being positioned normally above and out of contact with thesurface of the water and a second means being positioned normally belowthe surface of the water and in a protected or aft position on the boat.

A further object of this invention is to provide a hydrofoil boat withhydrofoil control means comprising wave detecting means normallypositioned above the surface of the water and operable to transmit an upcom mand when contact is made with the surface of the water andcavitation line detecting means normally extending beneath the surfaceof the water and operable to transmit a down command when the hydrofoilsreach the cavitation line.

A still further objectv of this invention is to provide a hydrofoilcontrol system for a hydrofoil boat including a downwardly extendingsurface detecting means normally out of contact with the water surfacebut which is urged aftof a downwardly extending position by contactthereof with the surface of the water for raising the boat.

applicaant er Patented Sept. 22, 1964 Another object of this inventionis to provide for a boat hydrofoil control system having a cavitationline detecting forwardly urged deflector means that is urged forwardlyfrom a downwardly extending position due .to a decreased impingement ofthe water against the deflector as the hydrofoil moves up to thecavitation line for lowering the boat.

Another object of this invention is to provide a hydrofoii control meansfor a boat wherein safety means is provided on at least one of thedownwardly extending control vanes whereby the vane is pivoted aft dueto contact thereof with foreign material in the water.

Another object of this invention is to provide a hydrofoil control meanswhich is retractable transversely out of the water.

Another object of this invention is to provide a hydrofoil control meanson a boat comprising linkage means interconnecting a surface detectingmeans and a cavitation line detecting means with controllable hydrofoilson the boat.

Another object of this invention is to provide a hydrofoil control meansComprising interconnecting linkage between a surface detecting means anda cavitation line detecting means for operating a single hydrofoil.

Other objects and various advantages of the disclosed hydrofoil boatwith wave and cavitation control means will be apparent from thefollowing detailed'description, together with the accompanying drawings,submitted for purposes of illustration only and not intended to definethe scope of the invention, reference being had for that purpose to thesubjoined claims.

Briefly, this invention comprises a hydrofoil boat with either one ortwo controllable hydrofoils connected to an automatically operated boatposition sensing means. One sensing means comprises a vane spring biasedto a downwardly extending position and normally positioned out of thewater when the boat is riding high enough to clear the waves and whichvane upon contact with the surface of the water when the boat has sunkbelow its operating range, produces a boat up signal to the controllablehydrofoils. The other boat position sensing means comprises a secondvane spring biased forwardly of'a downwardly extending position toprovide a boat down signal for lowering the hydrofoils out of thecavitation area when the boat has risen too high in the water. The boatis lowered until impingement of the water urges rearwardly and maintainsthe second vane in the downwardly extending position where no signal isgenerated. Safety means is disclosed for incorporation in the vanes forpreventing breaking and fracturing of the vanes upon contact withflotsam, retracting means is disclosed for incorporating in the vanesfor raising thereof, and a further safety feature of the control systemis disclosed wherein the vanes are so constructed that either may bemounted just aft of a protection strut or a hydrofoil support strut.

The drawings diagrammatically iilustrate by way of example, not by wayof limitation, at least two forms of the invention wherein likereferenced numerals designate corresponding parts in the several viewsin which:

FIG. 1 is a side view partly in section of a hydrofoil boat with thedisclosed hydrofoil control system thereon;

FIG. 2 is a detailed side view of the wave detecting means portion ofthe overall hydrofoil control system for raising the boat higher abovethe surface of the water;

FIG. 3 is a detailed side view, with parts cut away for clarity ofdisclosure, of the cavitation detecting means portion of the hydrofoilcontrol system for lowering the boat relative to the surface of thewater;

FIG. 4 is a schematic view of the linkage from both detecting means of ahydrofoil control system for operating two controllable hydrofoils;

FIG. is a schematic view of a hydrofoil control system for operation ofa Single controllable hydrofoil;

FIG. 6 is a detailed side view partly in section of a modified wavedetecting means, and;

FIG. 7 is a detailed side view partly in section of another cavitationdetecting means.

FIG. 1 discloses a typical hydrofoil boat in which the invention may beutilized wherein the boat 1% is supported by two controllablehydr-ofoils, a forward hydrofoil 11 and a rearward hydrofoil 12.

A boat up command forward Wave detecting or water surface detectingmeans 13 is shown connected or pivotally mounted on the bow of the boatand a boat down command cavitation line detecting means 14 is positionedon the aft end of the boat.

The boat up command water surface detecting means 13, FIG. 2, comprisesa vane or surface detecting means 15 pivotally mounted to the boat withpivot 15 and spring biased forwardly to the vertical position with atension spring 17 until stopped by a suitable projection or stop 18 onthe vane. The vane 15 is prevented from moving forwardly beyond thevertical position by the projection 18 contacting a portion 19 of thebow. Vane 15 is short enough whereby it does not normally contact thewater when the hydr-ofoils are submerged below the cavitation line fornormal cruising position as illustrated by the solid line forwardportion of FIG. 1. Accordingly in operation, when the boat sinks belowthe predetermined operating area as for example where it will becontacted by the waves as shown by the broken line forward portionof'FIG. 1, then the vane 15 or surface detecting means is struck by thewater and pivoted aft thereby causing an up command to be generated bythe linkage connected thereto described thereinafter for raising theboat, i.e., forward hydrofoil l]. is lowered, the resultant added liftof which causes the bow, and accordingly the whole boat to rise agreater distance above the water.

The boat down command cavitation line detecting means 14 comprises adownwardly extending vane or cavitation line detecting means 20connected to the stern of the boat by pivot 21. A tension spring 22 isconnected to the vane 24) below pivot 21 and a projection 23 ispositioned on the vane above the pivot so that the spring normally urgesthe vane forwardly from a vertical position to a forwardly extendingposition.

Upon the boat rising from the cruising solid line position of FIG. 1 tothe broken line position where the hydrofoils begin to approach thecavitation line, then the hydrodynamic pressure upon the vane it isdecreased such that the forces of the spring take effect and actuate thevane 20 forwardly to give a down signal to the hydrofoils. Thus, due tothe increased lift at the aft end of the boat caused by lowering ofrearward hydrofoil 12, the boat is controlled to sink downwardly untilthe hydrofoils are lowered well below the cavitation line for efficientoperation, and until the hydrodynamic pressure again forces vane 20rearwardly.

The detrimental results of cavitation is a reduction in the efliciencyof the foils and erratic operation of the boat.

.If pushed beyond the limit, the foil system will lose lift and thecraft will fall back into the water.

While a metallic helical spring is preferred in usage for the tensionspring means 17 and 22 for actuation of the respective forward and aftvanes, obviously other means may be utilized for actuating the surfacedetector and the cavitation line detector, such as but not limited to, abungee cord, an elastic plastic device, an air cylinder and accumulator,or a mechanical or electrical detecting and repositioning means, etc.,depending on the requirements of the particular hydrofoil boat.

While not a part of this invention, if the boat and/or the foil systemare not inherently stable, obviously suitable artificial pitch, yaw, androll stabilization means may be incorporated therewith.

A beam 24, FIG. 1, may be attached to the boat bottom immediatelyforward of the aft vane 20 as shown for protection of the beam.

The control mechanism for the forward hydrofoil 11 on forward strut 26is shown in FIGS. 2 and 4 wherein a boat up command link 27, FIG. 2, ispivotally connected between the top of vane and a bell crank 28, FIG. 4.Vertical link 29 is connected between the bell crank 28 and movableportion 30 of the forward hydrofoil 11.

In regard to the cavitation line vane detecting means 20, FIG. 3, a boatdown command link 31, FIGS. 3 and 4, is pivotally connected between topof vane 20, FIG. 3, and a second bell crank 32, FIG. 4. Vertical link 33I is pivotally connected between the bell crank 32 and the movableportion 34 of aft hydrofoil 12.

While the boat up and down command sensing means of the embodiment ofFIG. 4 is illustrated as operating two different hydrofoils, if sodesired, with different types of boats, particularly one having only onemovable hydrofoil, both sensing means may be connected to the singlehydrofoil. Such an alternate hydrofoil control means for operating asingle controllable hydrofoil 35 on a boat is shown in FIG. 5 whereinthe boat up command link 27 is pivotally connected between a surfacedetecting vane, such as vane 15, FIG. 1 and the upper end of an arm 35,FIG. 5, the arm being pivotally supported intermediate its ends onaxially slidable rod 37. Sleeve 38 which is fixed to the boat slidablysupports rod 37. Horizontal link 39 is pivotally connected between thelower end of arm 36 and a bell crank 46. Vertical link 41 is pivotallyconnected between bell crank 49 and movable portion 42 of 'the'singlehydrofoil 35, the latter hydrofoil being similar to forward hydrofoil11, FIG. 1.

' Also in FIG. 5, boat down command link 31 is pivotally connectedbetween the cavitation line vane detecting means 20 and the upper end ofan arm 43, the latter arm being pivotally supported intermediate itsends by pin 44 on fixed structure 45 on the boat. Horizontal link 51pivotally connects the lower end of arm 43 to the slidable rod 37 forupward actuation of the movable portion 42 of single hydrofoil 35causing the hydrofoil to dive deeper in the water away from thecavitation line. Thus with the single hydrofoil 35 positioned forwardlyof the boat similar to hydrofoil 11, FIG. 1, except the portion 42 isrequired to be movable both up and down, the boat is made to rise orfall, respectively, relative to the surface of the Water.

As shown in FIG. 3, vane 20 comprises two parts, 46 and 47,respectively, pivotally interconnected with pin 48. A tension spring 49interconnects the parts 46 and 4'7 of the vane 20 for urging the twoparts collinear. During normal hydrofoil operation, the two parts aremaintained collinear. Nevertheless upon contact with flotsam or otherfloating debris, the lower part 47 swings. back or is pivoted back aboutthe pivot pin 48 to thereby obviate fracture of the cavitation line vanedetection means 26. Obviously vane 15 may be so constructed if desired.

Likewise a second pivot pin 50, FIG. 3, positioned below pivot pin 48 ofvane 20 but normal thereto is provided for pivotally interconnecting twoportions 51 and 52, of lower part 47 whereby pivotal movement of the.lower portion 52 is transversely and upwardly for folding or retractingthe vane out of the water into a stowed position. The retracting meansfor folding lower portion 52 upwardly comprises any conventional motor,such as but not limited to a hydraulic actuator. Vane 15 also may be soconstructed if desired.

An alternate boat up command water surface detecting means 13a isdisclosed .in FIG. 6 wherein the surface detecting vane 15a is mountedto the boat immediately aft of the forward hydrofoil strut 26. Thelengths of the various linkage of the instant surface detecting means13:: are variedover that of the FIG. 5 embodiment in order to soposition the vane 15a aft of the strut for greater reliability ofcontrol of the forward hydrofoil 11 in the case h; of maneuvering aroundand contacting flotsam or'other floating debris.

Also for reasons of increased reliability of control of the afthydrofoil 12, FIG. 7 discloses a slightly varied linkage for positioningof the boat down command cavitation line detecting vane 20a immediatelyaft of the aft hydrofoil supporting strut 25. With the vane Zila thuspositioned relative to and combined with the aft hydrofoil strut 25,and/ or vane 15a, FIG. 6, positioned relative to and combined with thefore hydrofoil strut 26, operation of the boat in flotsam covered wateris of no detriment to the reliability of control and safety of the boat.

In the modification of FIG. wherein only one movable hydrofoil isutilized for control of the height of the boat above the surface of thewater, the features of the embodiment of FIGS. 6 and 7 may likewise becombined therewith, if so desired for various reasons. In this case thetwo sensing vanes could be attached to the boat or struts side-by-sideimmediately aft of the operable hydrofoil strut or attached in tandemaft of the strut, depending on the size of the particular strut and eddycurrents aft of the strut.

Accordingly a hydrofoil boat has been invented which includes a wave andcavitation control system connected to either one or to two movable andcontrollable hydrofoils and which may be constructed for mounting invarious positions relative to the hydrofoil struts. Hydrofoil controlmeans is disclosed comprising the wave detecting means normallypositioned above the surface of the water and operable to transmit aboat up command when contact is made with the surface of the water,thisup command being transmitted to either one or both hydrofoils. Also thedisclosed hydrofoil control means comprises a cavitation detecting meansnormally protruding beneath the surface of the Water and operable totransmit a boat down command to lower the boat when the hydrofoils havereached the cavitation line. Likewise it has been shown how either orboth of .the vanes may be combined in various manners With thehydrofoils for protection and increased reliability of control. Likewiseone or both of the hydrofoils may be formed in two pivotally connectedparts and spring biased'in such a manner that one part may be pivotedrearwardly upon contact with foreign material in the Water. Anadditional pivot may be added to either one of the vanes ,or bot-h ofthe vanes for transverse pivotal movement thereof from the water tostowed position. Likewise linkage has been shown with which either orboth vanes may be connected to either one or two controllablehydrofoils.

While only a few embodiments of the invention have been shown in theaccompanying drawings it will be evident that various othermodifications are possible in the arrangement and construction of thedisclosed hydrofoil boat.

I claim:

1. A hydrofoil boat comprising in combination, a boat, hydrofoil meansconnected to said boat and comprising at least two hydrofoils, saidhydrofoil means comprising means for raising and lowering the boatrelative to the surface of the water between a position wherein the boatis about to contact the surface of the water and a position wherein thehydrofoils are at or above a cavitation line where cavitation of saidhydrofoils may result, means for controlling said hydrofoil means, saidcontrol means comprising a water surface detecting means normallypositioned above the surface of the water and rotatable about athwartship axis when contact is made with the surface of the water,mechanical linkage means including a plurality of interconnected linksconnected directly to said water surface detecting means, saidmechanical linkage means being responsive to said water surfacedetecting means for transmitting a boat up command to said hydrofoilmeans, and a cavitation detecting means normally protruding beneath thesurface of the water and rotatable about a thwartship axis when saidhydrofoils reach the pivotally mounted directly on the bow of the boatin a position normally out of contact with the surface of the water androtatable about a thwartship axis, said surface detecting means beingresponsive to contact with the water by movement about said thwartshipaxis for operating one of said hydrofoils to raise the boat, and saidcontrol means comprising cavitation detecting means mounted on the boatin a position normally protruding beneath the surface of the water androtatable about a thwartship axis, said cavitation detecting means beingresponsive to movement of the hydrofoils to the cavitation line bymovement about said thwartship axis for operating one of said hydrofoilsto lower the boat.

3. A hydrofoil boat having at least two hydrofoils, control means formaintaining the boat above the surface of the water and for maintainingthe hydrofoils below the cavitation line, said hydrofoil control meanscomprising surface detecting means normally positioned out of con- .tactwith the water and rotatable about a thwartship axis and cavitation linedetecting means normally protruding below the surface of the water androtatable about a thwartship axis, mechanical linkage means between oneof said detecting means and one of said hydrofoils, said mechanicallinkage means comprising at least two interconnected links, said surfacedetecting means being responsive to contact of the surface detectingmeans with the Water for movement about said thwartship axis foroperating one of said hydrofoils for raising the boat, and saidcavitation line detecting means being responsive to movement of thehydrofoils to the cavitation line for movement about said thwartshipaxis for operating one of said hydrofoils for lowering the boat. i

4. Hydrofoil boat control means as recited in claim 3 wherein saidsurface detecting means comprises spring biased downwardly extendingmeans whereby the downwardly extending means is urged aft of adownwardly extending position by contact thereof with the surface of thewater for operating one of said hydrofoils for raising the boat.

5. Hydrofoil boat control means as recited in claim 3 wherein saidcavitation line detecting means comprises a deflector means springbiased forwardly of a downwardly extending position whereby thedeflector is urged forwardly of the downwardly extendin position due toa decreased impingement of the water against the deflector as thehydrofoil moves up to the cavitation line for operating one of saidhydrofoils for lowering the boat.

6. Hydrofoil boat control means as recited in claim 3 wherein one ofsaid detecting means comprises a downwardly extending means, saiddownwardly extending means comprising two hingedly connected collinearparts.

7. Hydrofoil boat control means as recited in claim 3 wherein one ofsaid detecting means comprises a downwardly extending means, saiddownwardly extending means comprising two hingedly connected portionswherein the lower part is pivotable upwardly for retraction thereof whennot in use.

8. A hydrofoil boat having a first controllable hydrofoil and a secondcontrollable hydrofoil, hydrofoil control means for maintaining the boatabove the surface of the water and for maintaining the hydrofoils belowthe cavitation line, said hydrofoil control means comprising surfacedetecting means normally positioned out of contact with the water androtatable about a thwartship axis and cavitation line detecting meansnormally protruding below the surface of the water and rotatable about athwartship axis, linkage means between said first controlamasoa lablehydrofoil and said surface detecting means, said linkage meanscomprising at least two interconnected links, linkage means between saidsecond controllable hydrofoil and said cavitation line detecting means,said surface detecting means being responsive to contact with the waterby movement about said thwartship axis for operating said firstcontrollable hydrofoil for raising the boat, and said cavitation linedetecting means being respon sive to movement of the hydrofoils to thecavitation line by movement about said thwartship axis for operatingsaid second controllable hydrofoils for lowering the boat.

9. A hydrofoil boat as recited in claim 8 wherein said surface detectingmeans comprises spring biased downwardly extending means whereby thedownwardly extending means is urged aft of a downwardly extendingposition by contact thereof with the surface of the water for operatingsaid first hydrofoil for raising the boat.

10. A hydrofoil boat as recited in claim 8 wherein said cavitation linedetecting means comprises a deflector means spring biased forwardly of adownwardly extending position whereby the deflector is urged forwardlyof the downwardly extending position due to a decreased impingement ofthe Water against the deflector as the hydrofoil moves up to thecavitation line for operating said second hydrofoil for lowering theboat.

11. A hydrofoil boat having a controllable hydrofoil, hydrofoil controlmeans for maintaining the boat above the surface of the water and formaintaining said controllable hydrofoil below the cavitation line, saidhydrofoil control means comprising surface detecting means normallypositioned out of contact with the Water and rotatable about athwartship axis and cavitation line detecting means normally protrudingbelow the surface of the water and rotatable about a thwartship axis,linkage means between said controllable hydrofoil and said surfacedetecting means and said cavitation line detecting means, said linkagemeans comprising at least two interconnected links, said surfacedetecting means being responsive to contact with the water by movementabout said thwartship axis for operating said controllable hydrofoil forraising the boat, and said cavitation line detecting means beingresponsive to movement of said controllable hydrofoil to the cavitationline by movement about said thwartship axis for operating saidcontrollable hydrofoil for lowering the boat.

12. A hydrofoil boat having a hull comprising,

(a) a boat having at least two hydrofoils thereon,

(b) first control means being mounted on said hull and, said firstcontrol means being normally positioned above the surface of the waterand rotatable on said hull about a thwartship axis, said first controlmeans generating for one of said hydrofoils a boat up signal uponswinging movement of said first control means about its thwartship axisdue to contact with the water, and

(0) second control means, said second control means normally protrudingbeneath the surface of the water and rotatable about a thwartship axis,said. second control means generating for one of said hydrofoils a boatdown signal upon swinging movement of said second control means aboutits thwartship axis due to decreased impingement with the water.

13. A hydrofoil boat as recited in claim 12 wherein,

(a) said swinging movement of said first control means is in an aftdirection, and

(b) said swinging movement of said second control means is in a forwarddirection.

14. A hydrofoil-boat as recited in claim 12 wherein,

(a) the same hydrofoil is controlled by both said first control meansand said second control means.

15. In the hydrofoil boat as recited in claim 12,

(a) one of said control means comprising two hinged ly connected parts,

([1) spring means biasing said parts to a collinear relationship witheach other during normal hydrofoil operation, and

(c) said spring means permitting pivotal movement of one of said partsrelative to'the other part when flotsam or floating debris isencountered.

16. In the hydrofoil boat as recited in claim 10,

(a) one of said control means comprising two hingedly connectedportions, and

(b) means for pivoting upwardly one portion relative to the otherportion for retraction thereof when not in use.

17. In the, hydrofoil boat as recited in claim 12,

(a) a plurality of struts being connected between said hull and saidhydrofoils, and

(b) one of said control means being positioned immediately aft of one ofsaid struts,

18. In the hydrofoil boat as recited in claim 17,

(a) said one of said control means being said first control means.

19. In the hydrofoil boat as recited in claim 17,

(a) said one of said control means being said second control means.

References Cited in the file of this patent UNITED STATES PATENTS2,576,716 Gardiner Nov. 27, 1951 2,584,347 Hazard Feb. 5, 1952 2,773,467Bailey Dec. 11, 1956 2,795,202 Hook June 11, 1957 3,104,642 Piazza Sept.24, 1963

1. A HYDROFOIL BOAT COMPRISING IN COMBINATION, A BOAT, HYDROFOIL MEANSCONNECTED TO SAID BOAT AND COMPRISING AT LEAST TWO HYDROFOILS, SAIDHYDROFOIL MEANS COMPRISING MEANS FOR RAISING AND LOWERING THE BOATRELATIVE TO THE SURFACE OF THE WATER BETWEEN A POSITION WHEREIN THE BOATIS ABOUT TO CONTACT THE SURFACE OF THE WATER AND A POSITION WHEREIN THEHYDROFOILS ARE AT OR ABOVE A CAVIATION LINE WHERE CAVITATION OF SAIDHYDROFOILS MAY RESULT, MEANS FOR CONTROLLING SAID HYDROFOIL MEANS, SAIDCONTROL MEANS COMPRISING A WATER SURFACE DETECTING MEANS NORMALLYPOSITIONED ABOVE THE SURFACE OF THE WATER AND ROTATABLE ABOUT ATHWARTSHIP AXIS WHEN CONTACT IS MADE WITH THE SURFACE OF THE WATER,MECHANICAL LINKAGE MEANS INCLUDING A PLURALITY OF INTERCONNECTED LINKSCONNECTED DIRECTLY TO SAID WATER SURFACE DETECTING MEANS, SAIDMECHANICAL LINKAGE MEANS BEING RESPONSIVE TO SAID WATER SURFACEDETECTING MEANS FOR TRANSMITTING A BOAT UP COMMAND TO SAID HYDROFOILMEANS, AND A CAVITATION DETECTING MEANS NORMALLY PROTRUDING BENEATH THESURFACE OF THE WATER AND ROTATABLE ABOUT A THWARTSHIP AXIS WHEN SAIDHYDROFOILS REACH THE CAVITATION LINE TO TRANSMIT A BOAT DOWN COMMAND TOSAID HYDROFOIL MEANS.